A fuel cell comprises a fuel electrode and an air electrode sandwiching an electrolyte. A fuel gas or the like is supplied to the electrodes to generate electricity. In a solid oxide fuel cell (SOFC), in particular, a fuel electrode (hydrogen electrode) and an air electrode (oxygen electrode) are joined to an electrolyte made of a solid oxide. The fuel electrode is supplied with a fuel gas and the air electrode is supplied with air or the like, whereby high-output electric power can be generated. The solid oxide fuel cell can use, as the fuel gas, not only hydrogen gas but a gas containing a large amount of carbon monoxide (e.g., exhaust gas of a motor vehicle driven by an internal combustion engine).
Such a solid oxide fuel cell is disclosed in Patent Document 1. In the disclosed fuel cell, the fuel and air electrodes are exposed to the internal spaces of respective different chambers to be supplied with hydrogen and oxygen, respectively. The solid oxide fuel cell with such a configuration is referred to as a dual-chamber type. In the case of arranging the dual-chamber SOFC in an exhaust pipe through which exhaust gas flows, hydrogen is let into the fuel electrode-side chamber by utilizing the flow of the exhaust gas, and oxygen is fed into the air electrode-side chamber by using a pump or the like.
It is not desirable, however, to use a pump or the like to supply the air electrode with oxygen contained in air, because the device as a whole is increased in size. The air electrode may be exposed to the atmosphere in order to dispense with the pump or the like, but from the standpoint of protection of the air electrode, the air electrode should preferably be arranged in a chamber. Accordingly, there has been a demand for methods whereby an air electrode arranged in a chamber can be efficiently supplied with oxygen contained in air without the need to use a separate air supply device.